Sizing system for high modulus fibers and method and apparatus for applying same



March 17, 1970 3,501,431 non AND J. H. ROSS EI'AL sxzwa SYSTEM FORHIGH MODULUS FIBERS my MET APPARATUS FOR APPLYING SAME Filed Nov. 25, 1966 m m a m M N NSS R ES 0 V G T N T 1RD A y m m MR Y B United States Patent 3 501,431 SIZING SYSTEM FOR HIGH MODULUS FIBERS AND METHOD AND APPARATUS FOR APPLY- ING SAME Jack H. Ross and Raymond G. Spain, Dayton, Ohio, as-

signors to the United States of America as represented by the Secretary of the Air Force Filed Nov. 25, 1966, Ser. No. 597,144 Int. Cl. C09d 3/78; C08f 45/52 US. Cl. 260-285 4 Claims ABSTRACT OF THE DISCLOSURE The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to us of any royalty thereon.

The present invention relates to a novel fiber and yarn sizing which is particularly adaptable for use on strands or filaments of high modulus brittle material such as carbon, graphite, other pyrolytic substances, metals and the like. The sizing of this invention is particularly useful in the processing of fibers .or filaments in the form of yarns that are to be woven into fabrics or otherwise bent or abraided in their use or processing. The present invention also relates to the method and apparatus for applying the sizing.

The textile arts have of late been substantially influenced by the development of a variety of fibrous and filamentous strands in the form of yarns, rovings or the like of high tensile strength, high elastic modulus materials such as carbon, graphite and a variety of pyrolytic substances, some of which are applied to metallic substrates. Because of their strength and refractory capabilities, such fibers, filaments and yarns are known to have great potential for use in aerospace deceleration systems, as protective garments, as flexible reinforcements in heat shields such as those employed in rocket engines, and as reinforcements for rigid ablative heat shields as for example upon the nose cones of aerospace re-entry vehicles or in the leading edges of high-speed aircraft.

In almost all of these potential applications however, it is preferred if not absolutely necessary, that the fibers or strands be woven into a fabric or otherwise interlaced or overlapped so that the strands are in contact with other similar strands or with successive turns or convolutions of themselves. Because such strands and/or the fibers of which they are composed have a relatively high modulus, are brittle, and exhibit relatively poor abrasion resistance, however, they have been most difiicult to manipulate during their processing and ultimate weaving or interlacing into fabrics. In some instances, the poor abrasion resistance continues to be a deleterious influence upon the structural stability of the fabric even after it is woven in that damaging strand-to-strand abrasion or fiber-to-fiber abrasion within the strands occurs during the normal bending and flexing thereof that is likely to be encountered in almost all of the uses to which the fabrics might otherwise be put. As a result of these weaknesses "ice and disadvantages, the new fibers, yarns and fabrics have been heretofore unemployable in many of the applications for which their other properties render them particularly useful and desirable.

It is accordingly an .object of this invention to provide a novel chemical system in the form of a sizing composition to be applied to strands comprising filaments or fibers of brittle material which will make it possible for them to be woven or otherwise formed into fabrics or to be bent or flexed during use without premature failure resulting from their poor abrasion resistance.

Still another object of the invention is to provide a method and apparatus for the application of such a sizing system to strands of brittle fibers.

To achieve these and other objects and advantages which will appear from a reading of the following disclosure, the present invention teaches the combination of an elastomeric material on the one hand and a waxy lubriciOus substance on the other in a solvent or solvent mixture in which both the elastomer and waxy substance are capable of going into complete solution. At the same time, it is essential that the wax and the elastomer be chemically and physically incompatible to the extent that, upon the release of the solvent, the wax will separate from the elastomer. When this solvent mixture is applied to strands of the type described above and the solvent is then driven off, the waxy component not only separates from the elastomeric material but also migrates toward the surface .of the elastomeric film about the fibers 'or filaments where it is capable of acting as a lubricant to reduce the effect of the abrasive forces which occur between them either during the weaving or the use thereof. A particular improvement which appears to be gained by this relative position of the lubricious wax, the elastomeric component and the fibers or filaments of which the strand is composed is the presence of the lubricant to reduce abrasion at the outer surfaces of the strand at which the greatest abrasive forces are likely to be encountered and the relative absence of the lubricant interiorly of the strand thereby inhibiting such interfilament or inter-fiber movement as would deleteriously affect the strands ultimate strength which of course depends in a large measure upon the interlocking engagement between the filaments or the fibers.

The materials to be employed as the elastomeric component of this sizing system are preferably chosen from that class which is characterized by a relatively high green strength; i.e., having a relatively high elastic modulus and tensile strength in the uncured state. Elastomers within this class capable of producing particularly improved results according to the present invention are the fluorinated elastomers such as Viton AHV which is a fluorinated copolymer of vinylidene fluoride and hexafluoropropene manufactured and sold under that proprietary name by E. I. du Pont de Nemours Co., Inc. of Wilmington, Del., the urethanes such as Estane which is a polyurethane manufactured and sold under that proprietary name .by the B. F. Goodrich Company of Akron, Ohio, and flexible vinyl chloride. The waxy component of the system on the other hand may be any of a variety of conventional Waxes such as paraflin or high molecular weight saturated hydrocarbon. As indicated above however, it is important that the selection of the elastomeric and waxy components to be employed in a particular system be such that the two are mutually incompatible while being at the same time soluble in the same solvent or solvent mixture so that they may be therein dissolved and applied as a sizing bath to the strands or yarns by conventional means such as immersion or spraying. Thereafter, the solvent is driven off, preferably at an accelerated rate as for example by the exposure of the impregnated strands to heated and/or rapidly moving air.

In a preferred modification of this invention, the nature of the elastomeric material employed and of the postimpregnation treatment is such that, in addition to the release of the solvent, the elastomeric material becomes cured within the fiber strand. It is of critical importance that the coated yarn prior to such curing be maintained free of contact with any surface such as drying racks or reels or spools that are normally used in the application of coatings. Upon the drying and/or curing, the sized yarn may be wound upon conventional spools or reels for supply to a loom or other weaving or interlacing mechanism or operation. During the drying and/ or curing stage, the waxy component, which, as above explained, remains chemically unattached to the elastomer, actively migrates to the surface of the elastomer especially at the outer strand surface there to provide a lubricating effect. The elastomer on the other hand, having penetrated the interstices between the fibers or filaments of the yarn, coats each of the fibers or filaments and thereby protects them from inter-fiber abrasion, not only during the weaving operation but also under that flexing which is encountered in the ultimate application of the fabric. In this manner the sizing system of this invention reduces the degradation that occurs as the otherwise brittle yarn moves over the bars in a weaving apparatus and through openings the ein where repeated rubbing or abrasion will occur. Consequently, the high modulus, high tensile strength refractory fibers and filaments that have been made available as such to the art can now be woven into fabrics thereby greatly expanding the areas of their potential use.

The invention thus generally described may be more clearly understood by reference to the following detailed description of certain specific embodiments and examples thereof in connection with which reference may be had to the appended drawing which is a schematic illustration of an apparatus for the application of the novel sizing composition of this invention to a continuous yarn or strand.

In one embodiment of this invention, fifteen parts by weight of a fluorinated elastomer according to the formula wherein x is approximately 4.5y admixed with one part by weight of a paraflin of the type having the formula C H in a two-solvent system compris ng equal weight amounts of methylethyl ketone and toluene. By way of specific example, thirty grams of the fluorinated elastomer and two grams of the paraffin are mixed as by stirring in a two-solvent mixture comprising 400 grams each of the methyl-ethyl ketone and of the toluene until the elastomer and the paraffin are completely dissolved. The sizing solution thus constituted is then applied to strands of the type herein considered by being placed in a reservoir or bath defined by the open tank or receptacle in which the sizing solution 11 is maintained at a relatively high level 12 as for example by conventional automatic flow control means involving float valves and the like (not shown). The yarn to be treated is taken from a conventional supply spool 13 from which, as a continuous strand 14, it passes over the guiding bar 15 and around the sheave or pulley 16, at least a substantial portion of which is submersed below the level 12 of the sizing solution 11 so that, as the yarn passes around and under the sheave, the individual filaments or fibers of the strand are coated and the interstices between them are filled with the sizing system. The varn thus coated and impregnated is then re- "moved from the bath 11 and caused to pass through the drying and/or curing tube or tower 17 which, in a specific embodiment may be an open ended hollow aluminum tube approximately six feet three inches in length with an inside diameter of one and one-eighth inches. Associated with the drying tube arethe guiding wheels or pulleys 18 and 19 at the bottom and top thereof respectively which are so positioned that, as the continuous strand 14 passes over them, it is held away from contact with any portion of the tube or any other surface therein while it is under the influence of the environment provided thereby. As the strand 14 passes around the uppermost guiding pulley 19, it is then led away from the drying tube as by being passed around the guiding bars or rollers 20 and 21 and onto a storage reel or spool 22 which may be rotatably driven by conventional means (not shown) so as to motivate the passage of the yarn through the immersion bath 11 and the drying tube 17.

Also associated with the drying tube in certain applications of the present invention may be an electrically energized resistance heating element 23 which is wound in a plurality of successive turns about the exterior of the tube. In a specific example, the resistance heating element 23 is operable at 110 volts and designed to consume 340 watts of electricity. Also associated with the drying tube and in fluid communication with the interior thereof at a point approximately one-third of its length from the top is a heater-blower unit 24 which, in one specific example, is capable of supplying air heated to a temperature of 500 degrees Fahrenheit. The air is led from the heater and blower component via the angularly disposed conduit 25 into the interior of the drying tube. The angular disposition of the conduit 25 is such that the direction of the air thus introduced is counter to the direction of the movement of the yarn.

Where the yarn is a carbon or graphite of one or two plies of 700 filament yarn having 7,000 yards per pound and chromel R Superalloy filaments 0.5 mil diameter twisted into a yarn and is sized with the above-described composition, it has been found that the desirable results sought by the present invention may be achieved where the yarn is caused, as for example by the driven speed of the winding spool 22, to move through the apparatus at a rate of 100 feet per minute so that it dwells for approximately 0.2 second within the sizing bath 11 and is within the controlled atmosphere of the heating tower 17 for approximately 3.7 seconds, and the heater-blower unit 24 and the heating element 23 are so actuated and energized as to provide a temperature within the tube of from 280 degrees to 320 degrees Fahrenheit with the air within the tube moving in a direction opposite that of the strand at the rate of 200 lineal feet per second. Under these conditions, it has been found that, during the time that the impregnated yarn travels from the lower pulley 18 to the pulley 19 at the top of the drying tube, the solvent will have been entirely evaporated and driven off, the elastomeric material according to the above formula such as the Viton AHV will have been substantially completely cured and the paraflin will have commenced its migration to the surface of the elastomeric coating. This migration will continue as the yarn is stored and will be somewhat accelerated during the subsequent flexing or bending of the yarn as in the case of its being woven.

As a demonstration of the results achieved by the present invention, various yarns were subjected to a test wherein they were passed over a one inch diameter bar and through a heddle eye of the type normally employed in looms for ten cycles with a 200 gram weight on one end of the yarn after which its breaking strength was determined. The yarn which was employed in the above-described specific example was subjected in its completely untreated condition (as it was received from the supplier) to the described test after which it was found to have a breaking strength of 5.5 pounds. Where the same yarn was coated according to the method and in the apparatus described, but with a sizing consisting only of the fluorinated elastomer; i.e., without any waxy ingredient therein, and was applied to the same test, it was found that its breaking strength improved to 11.5 pounds. Where however the parafiin and fluorinated elastomeric components were both employed in the sizing system and the yarn was treated according to the method and in the apparatus described, it was found upon such testing to have a breaking strength of 12.7 pounds. In a variety of similar tests with similarly treated strands and yarns of carbon, graphite, metallic and other relatively brittle high modulus, high tensile strength materials, it was found that, whereas the yarns or strands treated according to the present invention retained from 95 to 100 percent of their original strength after subjection to abrasion on the test above described or upon comparable tests, the yarns and strands not so treated would lose up to 50 percent of their original strength upon exposure to the same test conditions.

While the within invention has been described in considerable detail in connection with certain specific embodiments thereof, it is to be understood that the forego-' ing particularization has been for the purpose of illustration only and does not limit the scope of the invention as it is defined in the subjoined claims.

We claim:

1. A sizing composition for brittle strands which are to be woven of flexed comprising:

(a) an elastomeric component characterized by the formula H F F F E l IEI 1i CF: y

wherein x is approximately equal to 4.5y;

(b) paraffin; and

(c) a solvent in which said elastomeric component and said paraffin are dissolved; said parafiin and said elastomeric component being physically and chemically incompatible.

2. A sizing composition according to claim 1 wherein said paraflin is characterized by the formula C H wherein x is approximately equal to 4.5y;

(b) a waxy component such as parafiin or high molecular weight saturated hydrocarbon; and

(c) a solvent in which said elastomeric component and said waxy component are both soluble; said waxy component and said elastomeric component being physically and chemically incompatible.

References Cited UNITED STATES PATENTS 1/1966 Willicks et al. 26028.5 5/1967 Annonio et al.

MORRIS LIEBMAN, Primary Examiner SAMUEL L. FOX, Assistant Examiner US. Cl. X.R. 

